DOSBox

My kids like to play games from the 80s and early 90s when DOS was king. Ironically, Windows XP and Vista do not run nearly as many DOS games (even in their compatability modes) as DOSBox does. I have played DOS games (like the Xeen series) on both Windows and Linux boxes using DOSBox. There is a 10-minute learning curve as you figure out how to mount your real hard-drive to your "DOS" system, then it is smooth sailing.

It played all my games smoothly, brought back the nostalgia. There are a lot of configurable options, including nice upscaled rendering with clever algorithms. I only miss save/load machine state feature.